This was my iOS app configuration in Firebase console:
After the april 2020 update I did not receive notifications anymore.
So I decided to go for the APN auth key instead.
Go to your Apple developer account and create a P8 file.
You just have 1 key for all your Apps and it can only be downloaded
1 time, so save it in a place where you can find it again.
Then upload it to Firebase:
Now the notifications is working again.